The present invention relates to a rhythm unit employed in association with an electronic organ or the like, and more particularly, to a rhythm unit having a control system that enables the opertor to determine which one of a combination of simultaneously played rhythm patterns will be played as the pedal pattern.
It is conventional in electronic organs to provide a rhythm unit in the form of a repetitively operating pulse generator or the like, for continuously producing series of timed pulses in repetitive cycles. The heart of a typical rhythm system is a read only memory, or ROM, which has a plurality of input terminals connected individually to a like plurality of rhythm select switches and under control of a clock produces a series of pulses on an output line which are spaced to define the rhythm selected by the rhythm select switches. The commercially availabe Type M253 ROM typically used in rhythm units is a mask programmable ROM having twelve input terminals and eight output terminals (in addition to a clock terminal and the normal voltage terminals) and is capable of storing twelve different rhythm patterns. A source of clock pulses is connected to the clock terminal and when any of the input terminals is grounded by actuation of the corresponding rhythm select switch a rhythm pattern determined by the contents of the ROM appears as an 8-bit word on the output terminals. The eight bits of each word may correspond to eight percussive rhythm instruments such as bass drum, snare drum, cymbal, etc. Although there is seldom need for more than twelve rhythm patterns, it frequently is desirable to provide more than eight percussive rhythm instruments; heretofore this objective has been achieved by utilizing two such ROM's, connecting the twelve rhythm select switches in parallel to corresponding input lines of the two ROMs, and controlling them with a common clock thereby to provide twelve possible patterns on sixteen instrument output lines. Applicant's assignee uses this arrangement in certain of its current organ models, utilizing the sixteen available output lines to feed up to sixteen instruments, including the "Walking Bass" outputs and accompaniment rhythms, in addition to a variety of percussive instruments. With this arrangement, when two or more rhythm patterns are on, the outputs from both ROMs "OR". Whenever there is a bass drum beat, for example, in either of the on rhythm patterns, it will also appear in the "new" combination pattern. This is acceptable, and in many cases quite useful, in the case of percussive rhythm instruments because it enables derivation of new patterns having certain characteristics of the selected patterns. However, the arrangement is not without its disadvantages. Not only do the normal rhythm patterns combine when two or more rhythm patterns are selected, but the accompaniment rhythm patterns and the "Walking Bass" pattern also combine which sometimes results in patterns that are not musically correct for either of the rhythm patterns, and the accompaniment rhythm pattern turns out to have a pattern with too many beats, one that is too busy.
Competitors of applicant's assignee have partially overcome this disadvantage by establishing a sequence of patterns left to right such that for any combination of selected rhythm patterns only the one to the left or to the right, as displayed on the rhythm select switches, will play. This solution, however, limits operation to a predetermined set of conditions so that if, for example, three rhythm patterns are turned on, the rhythm instruments may or may not sum but the pedal or "Walking Bass" patterns will be predetermined to be the farthest left in that group of three patterns; that is, only when the farthest left rhythm select switch is on can the "Walking Bass" pattern be obtained.